Exemplary embodiments of the present invention relate to a friction compensation logic of motor driven power steering (MDPS) and a friction compensation method using the same, and more particularly, to a friction compensation logic of MDPS and a friction compensation method using the same capable of calculating a friction compensation torque by separating sections set by friction at the time of driving the MDPS and reflecting the calculated friction compensation torque at the time of controlling an MDPS motor.
Generally, a motor driven power steering (hereinafter, referred to as ‘MDPS’) system is a system which does not generally use a principle of operating a power handle by circulating oil by driving a power pump, but operates the power handle by operating a steering motor at the time of starting a vehicle by driving the steering motor for generating a steering force which is separately mounted at a lower end of a steering wheel shaft.
In order to smoothly operate the MDPS system, the MDPS system calculates a motor torque command by adding/subtracting a torque control loop, a damping torque active restoration torque, and a friction compensation torque at the time of calculating the motor torque command, in which the reason of adding friction compensation torque is as follows.
Generally, in the MDPS system, when the steering motor does not generate a required assist steering force by friction generated when each steering component is driven, the driving of the power handle by the steering motor is not easy, such that a sense of steering or a sense of initial build-up may deteriorate, thereby making a driver feel a sense of difference in steering.
Further, as an on-center column torque is excessive due to the friction, torque variation is excessive, such that an artificial sense of build-up may occur.
Therefore, a development of a friction compensation logic of MDPS to reduce the friction of the MDPS system is urgently required.
Background Art of the present invention is disclosed in Korean Patent Laid-Open Publication No. 10-2012-0053300 (Published on May 25, 2012, Title of The Invention: System For Control Motor Driven Power Steering Of Vehicle And Method Thereof).